A tooth that is damaged by caries, abrasion, etc. is, usually, directly restored by using a composite resin from the standpoint of aesthetic appearance, simple and quick operation when a cavity that is formed therein is still in the initial to intermediate stage and is small. On the other hand, a relatively large cavity is restored, usually, by using a prosthetic made of a metal, ceramics or a dental resin.
The dental restorative such as the composite resin or the prosthetic basically has no adhesive property to the tooth. Usually, therefore, use is made of an adhesive material comprising a polymerizable monomer composition for adhering the dental restorative to the tooth. The polymerizable monomer used for the adhesive material, usually, comprises a methacrylate type monomer as a chief component but its adhering force to the tooth is not satisfactory. When adhering the composite resin, for instance, the adhering strength is not, in many cases, large enough to overcome the internal stress that generates at the time when the composite resin is cured, i.e., is not large enough to overcome the tensile stress that occurs in the interface between the tooth and the composite resin. Besides, the adhering strength is not, in many cases, large enough to withstand the force produced by occlusion. In order to improve the adhering strengths of these adhesive materials, therefore, the following pretreatments have been conducted for the tooth surfaces at the time of using the adhesive materials.    1) Application of a pretreating material for etching a hard tooth (enamel comprising chiefly hydroxyapatite); and    2) Application of a pretreating material called primer for accelerating the permeation of the adhesive material into the tooth.
Under such circumstances, attempts have been made to develop a dental adhesive material containing a polymerizable monomer having adhesive property to the tooth in order to attain a larger adhering strength while reducing complexity of operation. For instance, higher adhering strengths have been expressed by using, at least as part of the polymerizable monomer component, a polymerizable monomer (hereinafter referred to as acid group-containing polymerizable monomer) containing an acid group such as phosphoric acid group or carboxylic acid group having high affinity to the tooth (hydroxyapatite or collagen) (patent document 1 and patent document 2).
There has also been reported that the adhering strength can be improved by using a phosphoric monoester monomer as an acid group-containing polymerizable monomer in the form of a metal salt with calcium or the like (patent document 3). Attempts have also been made to add a polyvalent metal ion-eluting filler to an adhesive material or primer that contains an acid group-containing polymerizable monomer and water to further improve its curability by polymerization (patent documents 4 to 7). Here, the polyvalent metal ion-eluting filler stands for a filler such as fluoroaluminosilicate glass that elutes out metal ions in an acidic solution. As polyvalent metal ions eluted out therefrom, there can be exemplified ions of such metals as alkaline earth metals, aluminum, etc. As the polyvalent metal ion-eluting filler, there has also been used a filler by substituting titanium or zirconium for part of the aluminum. However, there is found no Working Example that really uses ions of an element of the Group IV, and the amount of adding them has not been concretely taught, either. The reason why the adhesive material containing the polyvalent metal ion-eluting filler exhibits improved adhering strength is attributed to that when the adhesive material cures, the polymerizable monomer containing the acid group-containing polymerizable monomer undergoes the polymerization and, at the same time, polyvalent metal ions eluted out from the polyvalent metal ion-eluting filler form a salt with the acid group of the acid group-containing polymerizable monomer, whereby ionic crosslinking takes place enabling the strength of the cured body to be enhanced.